Scientists analyze optimum load rate for vinasse-to-biogas system

A team of Mexican scientists recently published the results of a study that aimed to determine the optimum organic loading rate for operating an upflow anaerobic sludge blanket (UASB) reactor to generate biogas using waste from sugarcane ethanol production. A paper outlining the study, titled “Methane production by treating vinasses from hydrous ethanol using a modified UASB reactor,” was published in the scientific journal Biotechnology for Biofuels.

According to the paper, between 9 and 14 liters of vinasse are generated for each liter of ethanol that is produced. While the material’s high nutrient and organic matter content have led to its use as fertilizer, the researchers point out that the presence of phytotoxic, antibacterial and recalcitrant compounds such as phenols, polyphenols and heavy metals can cause negative effects on the environment in discharge areas. “It is therefore necessary to subject this waste to a conditioning treatment prior to its disposal in the environment,” the team said in the report.

The researchers point out that UASB reactors are the most popular anaerobic digester. Some of the primary advantages of the system are its high treatment capacity, low sludge production and conversation rate of more than 50 percent chemical oxygen demand (COD) to biogas.

According to the researchers, the study determined that the optimum load rate was 17.05 kg COD/cubic meter per day, which corresponded to the highest biogas methane content—84 percent. When the organic load rate (OLR) was increased to 22.16 kg COD/cubic meter per day, the system collapsed.

A full copy of the peer reviewed paper can be downloaded from the Biotechnology for Biofuels website.